Sn-doped In2O3 thin films [In2-xSnxO3: ITO] exhibit a remarkable combination of optical and electrical transport properties. These include a low electrical resistivity, which is typically in the order of 10−4 Ωcm. This property is related to the presence of shallow donor or impurity states located close to the host (In2O3) conduction band, which are produced by chemical doping of Sn+4 for In+3 or by the presence of oxygen vacancy impurity states in In2O3-x. The films also exhibit high optical transparency (>80%) in the visible range of the spectrum (P. P. Edwards, et al.; Dalton Trans., 2004, 2995-3002).
Transparent conductive coatings or layers which comprise ITO have many applications, including in liquid crystal displays, flat panel displays (FPDs), plasma displays, touch panels, electronic ink applications, organic light-emitting diodes, electroluminescent devices, optoelectronic devices, photovoltaic devices, solar cells, photodiodes, and as antistatic coatings or EMI shieldings. ITO is also used for various optical coatings, most notably infrared-reflecting coatings (hot mirrors) for architectural, automotive, and sodium vapor lamp glasses. Other uses include gas sensors, antireflection coatings, electrowetting on dielectrics, and Bragg reflectors for VCSEL lasers. Furthermore, ITO can be used in thin film strain gauges. ITO thin film strain gauges can operate at temperatures up to 1400° C. and can be used in harsh environments.
Due to the cost and scarcity of indium metal, the principle component of ITO, a stable supply of indium may be difficult to sustain for an expanding market for flat panel displays, solar cells and other applications. There is therefore an ongoing need to reduce the amount of indium or produce indium-free phases as alternative transparent conducting materials for transparent conductor applications.